Till now the radio communication system has been developed rapidly. The original second generation mobile communication system, i.e., the Global System for Mobile Communications (GSM) system is continuously evolved to techniques such as General Packet Radio Service (GPRS) and Enhanced Data Rate for GSM Evolution (EDGE), thereby greatly improving the data transmission capability of the system. The third generation mobile communication system has a higher transmission rate, adopts techniques such as Wideband Code Division Multiple Access (WCDMA) and CDMA 2000, and is successively deployed and put into commercial operation in many countries and regions all over the world. With the development of the cellular communication technique, some other radio access techniques such as Wireless Local Area Network (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX) techniques are also developed quickly. In addition, projects such as the IEEE 802.16m technique for the fourth generation mobile communication system, the Third Generation Partnership Project Long Term Evolution (3GPP LTE) and the 3GPP LTE-Advanced are also started and being developed.
The Multiple Input Multiple Output (MIMO) multi-antenna system supports parallel transmissions of data streams, and greatly increases the system throughput, thus it garners particular attention in the academic researches and actual systems. Under normal circumstances, first of all, the forward error correction coding is independently performed for the parallel data streams in the multi-antenna transmission, and then the coded code words are mapped to one or more transmission layers. In case the code words are mapped to multiple transmission layers, a serial-to-parallel conversion of the serial data output from the coder is performed for multiple transmission layers. In one transmission, the number of transmission layers supported by the system is also referred to as the rank of the system.
Generally, the number of transmission layers supported by the multi-antenna system, i.e., the rank, is less than or equal to the number of the physical antennas of the multi-antenna system. The process of converting the data in each transmission layer into the data in each physical antenna is called as a signal pre-coding process. Particularly, the process of converting the data in each transmission layer into the data in each physical antenna through a linear operation is called as a signal linear pre-coding process. In the current radio communication system (e.g., the LTE system and the WiMax system), due to the limitations of the computational complexity and the signaling control complexity of the system, a certain number of pre-coding matrixes shall be designed for the system in advance. The set of the pre-coding matrixes is called as the pre-coding matrix codebook, in which the number of the pre-coding matrixes is called as the size of the pre-coding matrix codebook. In the multi-antenna system, the pre-coding matrix codebook, including the size and elements thereof, can directly influence the system indexes such as the throughput. Therefore, in order to improve the system performance (e.g., maximize the throughput), the pre-coding matrix codebook (including the size and pre-coding matrix elements thereof) used in the multi-antenna system shall be meticulously designed.
The pre-coding matrix codebook is composed of one or more pre-coding matrixes. Therefore, when the pre-coding matrix codebook and the pre-coding matrix codebook group is to be designed, the universal set of pre-coding matrixes shall be firstly acquired, so as to select therefrom the pre-coding matrixes for generating the pre-coding matrix codebook and the pre-coding matrix codebook group. There are various related arts to implement the universal set of pre-coding matrixes meeting the design conditions.
Each pre-coding matrix in the universal set of pre-coding matrixes may have the following form: [1, 1, . . . 1; x11, x12; . . . ; x1q; x21, x22, . . . , x2q; . . . ; . . . ; . . . ; xp1, xp2, . . . , xpq], wherein p is an integer and 1≦p≦P, q is an integer and 1≦q≦Q, P is the number of the transmitting antennas of the communication system, and Q is the rank of the communication system. As mentioned above, in one transmission, the number of all transmission layers supported by the system is referred to as the rank of the system. The universal set of pre-coding matrixes in other forms may also be used to provide the pre-coding matrixes for generating the pre-coding matrix codebook and the pre-coding matrix codebook group.
For the convenience of description, the 4-antenna system is taken as an example to illustrate the composition of the universal set of pre-coding matrixes. In such a system, the number of the layers supported by the system may be 1 to 4, i.e., the rank is 1 to 4.
For example, when the rank is 1, the form of a pre-coding matrix p is [1; x11; x21; x31]. The universal set of pre-coding matrixes for example may be formed by one or more of the following pre-coding matrixes meeting the above form.
4 pre-coding matrixes can be obtained from the Discrete Fourier Transform (DFT) matrix, wherein each of the pre-coding matrixes is corresponding to each column in the DFT matrix.
4 pre-coding matrixes can be obtained from the Hadamard matrix, wherein each of the pre-coding matrixes is corresponding to each column in the Hadamard matrix.
In addition, x11, x21, x31 may be QPSK, 8PSK or 16PSK constellation points or constellation points of higher dimensions.
For example, when x11, x21, x31 are QPSK constellation points, totally 4×4×4=64 pre-coding matrixes meeting the above form are obtained.
For another example, when x11, x21, x31 are 8PSK constellation points, totally 8×8×8=512 pre-coding matrixes meeting the above form are obtained.
For still another example, when x11, x21, x31 are 16PSK constellation points, totally 16×16×16=4096 pre-coding matrixes meeting the above form are obtained.
Of course, there may be other form of pre-coding matrixes with the rank=1.
Upon the system request, the pre-coding matrixes of one, several or all of the above forms or the power normalized matrixes thereof may be taken as the universal set of pre-coding matrixes with the rank=1.
In another example, when the rank=2, the form of the pre-coding matrix p is [1 1; x11 x12; x21 x22; x31 x32]. Similarly, the universal set of pre-coding matrixes may be formed by one or more of the following pre-coding matrixes meeting the form. In addition, as an example p is a unitary matrix, i.e., pH×p=αI, wherein α is a scalar.
6 pre-coding matrixes can be obtained from the DFT matrix, wherein each of the pre-coding matrixes is corresponding to two columns selected from the DFT matrix.
6 pre-coding matrixes can be obtained from the Hadamard matrix, wherein each of the pre-coding matrixes is corresponding to two columns selected from the Hadamard matrix.
In addition, x11 x12 x21 x22 x31 x32 may be QPSK, 8PSK or 16PSK constellation points or constellation points of higher dimensions.
For example, when x11 x12 x21 x22 x31 x32 are QPSK constellation points, totally 288 pre-coding matrixes meeting the above form are obtained.
For another example, when x11 x12 x21 x22 x31 x32 are 8PSK constellation points, totally 5376 pre-coding matrixes meeting the above form are obtained.
For still another example, when x11 x12 x21 x22 x31 x32 are 16PSK constellation points, totally 92160 pre-coding matrixes meeting the above form are obtained.
Of course, there may be other form of pre-coding matrixes with the rank=2.
Upon the system request, the pre-coding matrixes of one, several or all of the above forms or the power normalized matrixes thereof may be taken as the universal set of pre-coding matrixes with the rank=2.
The conditions of rank=3 and rank=4 are similar to the above conditions, and herein are not repeated.
In case of other antenna configurations, such as 2-antenna system, 8-antenna system or higher antenna system, the process of forming the universal set of pre-coding matrixes is similar to the process for the 4-antenna system, and herein is not repeated.
In different designs, there may be different forms of pre-coding matrixes for the same rank. For example, in case of the rank=3, there may be two different types of pre-coding matrixes, i.e., the Cubic Metric Preserving (CMP) pre-coding matrixes and the Cubic Metric Friendly (CMF) pre-coding matrixes.
When the CMP pre-coding matrixes are used, the CM value is lower, but the system performance is worse. On the other hand, when the CMF pre-coding matrixes are used, the CM value is higher, but the system performance is better. Thus for the actual system, corresponding pre-coding matrixes shall be extracted from the universal set of CMP pre-coding matrixes and the universal set of CMF pre-coding matrixes, respectively, to form the final codebook.
During the study of the present invention, the inventor finds that the following method that is easily conceivable usually cannot achieve the optimum codebook: forming a codebook by combining a predetermined number of best pre-coding matrixes extracted from the universal set of CMP pre-coding matrixes with a predetermined number of best pre-coding matrixes extracted from the universal set of CMF pre-coding matrixes. The inventor finds that this at least because the predetermined number of best pre-coding matrixes extracted from the universal set of CMP pre-coding matrixes and those extracted from the universal set of CMF pre-coding matrixes may be overlapped with each other or cannot optimally matched with each other, thus the formed codebook is not the optimum.
To be noted, although the above contents are arranged in the Background section so that a person skilled in the art can clearly understand the object of the present invention, it shall be appreciated that the above contents are not certainly well known to a person skilled in the art. It shall not be deemed that these contents are known by a person skilled in the art just because they are described in the Background section.
Literatures related to the related art and helpful to understand the present invention are listed as follows, and incorporated herein by reference, as if they were completely illustrated herein.    (1) European patent publication No. EP1919097A1 Codebook generator, codebook and method for generating update matrices to be used in a precoding scheme with MIMO transmission    (2) US patent publication No. US2008080449A1 Generalized codebook design method for limited feedback systems    (3) US patent publication No. US2008165876A1 APPARATUS FOR GENERATING PRECODING CODEBOOK FOR MIMO SYSTEM AND METHOD USING THE APPARATUS    (4) US patent publication No. US2008292013A1 NESTED PRECODING CODEBOOK STRUCTURES FOR MIMO SYSTEMS    (5) US patent publication No. US2008303699A1 MIMO wireless precoding system robust to power imbalance    (6) US patent publication No. US2008316910A1 Complex vector quantization codebook for use in downlink multi-user MIMO mobile broadcast systems    (7) US patent publication No. US2009006518A1 Simple MIMO precoding codebook design for a MIMO wireless communications system    (8) International patent publication No. WO2008086239A1 PRECODING CODEBOOK FOR MIMO SYSTEMS    (9) International patent publication No. WO2008097035A1 CODEBOOK GENERATING METHOD AND APPARATUS FOR GENERATING A CODEBOOK FOR MULTI-POLARIZED MULTIPLE-INPUT MULTIPLE-OUTPUT (MIMO) SYSTEMS    (10) International patent publication No. WO2008137523A1 A CODEBOOK METHOD FOR MULTIPLE INPUT MULTIPLE OUTPUT WIRELESS SYSTEM